Cigarette smoking is a prevalent, modifiable risk factor for increased morbidity and mortality in the United States, and perhaps in the world. Smokers incur medical risks attributable to direct inhalation. Bystanders, termed passive smokers, also incur medical risks from second-hand smoke. Society, as a whole, also bears the economic costs associated with death and disease attributable to smoking. Although the majority of smokers have tried repeatedly to quit smoking, eighty percent of smokers return to tobacco in less than two years after quitting. Therefore, tobacco dependence is a health hazard for millions of Americans.
Nicotine is the principal alkaloid in tobacco and is primarily responsible for tobacco dependence. The initiation and maintenance of tobacco dependence in a human is due to certain bio-behavioral and neuromolecular mechanisms. Nicotinic acetylcholine receptors (nAChRs) in humans are the initial binding sites for nicotine. The binding of nicotine to nAChRs modulates the brain's “reward” function by triggering dopamine release in the human brain.
Although a variety of psychopharmacological effects contribute to the reinforcing action, the existence of a mesolimbic dopaminergic pathway for nicotinic reward is the predominant hypothesis. The mesolimbic dopaminergic pathway originates in the ventral tegmental area (VTA) of the midbrain and projects to forebrain structures including the prefrontal cortex and to limbic areas such as the olfactory tubercle, the amygdala, the septal region, and the nucleus accumbens. Many studies have indicated that dopamine release in the nucleus accumbens of the human brain is “rewarding” or signals an encounter with a “reward” from the environment. Other substances, such as alcohol, cocaine, and opiates, operate in the same manner, resulting in a cycle of substance or alcohol abuse.
Therefore, a need exists for a novel compound that can block the dopamine release system to abolish nicotinic stimulation or smoking-induced “rewarding” and/or can block nAChRs to limit increasing nicotine-induced dopamine release.